These are four known methods of improving the wear and pitting resistant properties of cast iron products. One is surface treatment such as chromium-plating, nickel plating, and soft nitriding. Another is metallizing with molybdenum or iron. These two methods are highly effective for increasing the wear resistance but the production cost is high on account of the complicated processes involved. A third method is induction hardening or flame hardening. This method is relatively easy to carry but cannot yield sufficient wear resistance. A fourth method is chilled casting using a chiller in the mold. Since it is easy to carry out and considerably improves the wear resistance, this method is widely used; but castings which must serve under extremely severe conditions such as the camshafts, valve-lifters or valve rocker-arms of engines, etc., which have been produced by this method, have been found lacking in wear resistance and pitting resistance and are often found unsatisfactory with respect to pitting and wear.
There is also a known "hardenable" cast iron which is a kind of gray cast iron including small additions of alloying elements such as chromium, molybdenum, nickel, etc.; this is said to possess high pitting resistance; but when applied in a small, fast-running engine of the type produced in Japan, it wears badly and its resistance to pitting cannot be called satisfactory. This hardenable cast iron is characterized in that since it contains cementite and graphite half crystallized in the as-cast state, the matrix can be given a hardened structure through induction hardening or flame hardening; but even this hardened structure is not completely satisfactory with respect to pitting resistance.